DE 102004058472 A1 discloses a safety device and a method for determining an overtravel distance in a machine in which a first machine part executes an operating movement against a second machine part. In this case the machine includes at least a first and a second optical barrier. The two optical barriers accompany the first machine part in the operating movement. Here the first optical barrier runs ahead of the first machine part at a first distance, and the second optical barrier is arranged at a second distance from the first optical barrier. Also present is a control unit which is designed to stop the operating movement of the first machine part if the first optical barrier is interrupted. Also provided are a test unit and a blocking unit whereby, with the aid of the test unit, it is possible to check whether the second optical barrier is interrupted after the first machine part has stopped. The blocking unit serves to block the operating movement, depending on the test result from the test unit.
In DE 102004058472 A1, reference is made to DE 202 17 426 U1, which is concerned with the determination of the overtravel distance of the tool when the drive unit is shut down, and for this purpose discloses the use of a CNC control and the associated distance measuring system. DE 102004058472 A1 sees as a disadvantage of this procedure the considerable cost of ensuring reliable determination and monitoring of the overtravel distance complying with the relevant safety provisions, in particular European standard EN 954-1.
WO 01/92777 A1 discloses a protective device for machines such as bending presses, in which a first machine part executes operating movements against a second machine part, with a photoelectric barrier arrangement positioned between the machine parts and attached to the movable machine part, with a stop device for stopping the operating movement of the movable machine part if the light beam is interrupted, and with a deactivation device which deactivates the stop device at least immediately before a light beam interruption by the other machine part, wherein a speed measuring device is provided for the movable machine part, and the deactivation device has means for at least partial deactivation of the stop device below a presettable limit sped, and wherein a control unit for the operating movement of the movable machine part reduces the speed below the limit speed immediately before a light beam interruption by the other machine part.
EP 2 644 962 A1 discloses a forming apparatus in which information from a distance measuring system which is located at a lower safety level is confirmed with the aid of local information provided by targeted evaluation of suitably arranged photoelectric barriers, wherein the photoelectric barriers and the associated evaluation unit are located at a higher safety level, in order to allow a machine control to decide whether to switch from a fast tool movement to a slow tool movement and whether suppression of safety-oriented photoelectric barriers is possible.